The goals of the continuation of these studies are the attainment of the low resolution structure of the yolk lipoprotein complex from amphibian oocytes and a high resolution structure of mitochondrial malate dehydrogenase from porcine heart. Structural data on the microcrystalline yolk lipoprotein complex is being obtained from negatively stained electron micrographs. Plans for measuring the x-ray structure factors (to about 30 A resolution) from the x-ray powder photographs have also been made and some preliminary studies initiated. The model of the yolk lipoprotein will be first derived from a map calculated by the three-dimensional digital reconstruction method using between six and nine different views of projections of the lattice (6-9 different EM lattice views). In addition, some preliminary data has been obtained which indicates that some of the lipid can be extracted from the lipoprotein complex while maintaining the crystalline nature of the lattice. This means that it should be possible to obtain a model of the lipoprotein complex minus most of its lipid. Thus by difference, it should be possible to locate the lipid binding regions in the low resolution model of the lipoprotein complex. The studies on the structure of mitochondrial malate dehydrogenase are still at their early stages. Although we have recently determined the space group and unit cell dimension of m-MDH, a suitable supply of good crystals is not yet available. This portion of the project centers therefore on finding improved methods of purification and crystal preparation prior to the x-ray diffraction analysis. Several new purification steps have been found which significantly reduces the time involved in isolation of m-MDH and appear to reduce contamination by small amounts of mitochondrial aspartate amino transferase. When a reasonable supply of suitably large crystals are available, the usual single crystal methods will be used for structural studies. The long range goal will be to compare the molecular structure of m-MDH with its cytoplasmic counterpart, s-MDH.